1. Field of the Invention
My invention is concerned with a heat-exchanger for arrangement behind the combustion chamber of a heating boiler, and is further concerned with a method of manufacturing a heat-exchanger of this type.
2. Description of the Prior Art
Heat-exchangers of this type which are, however, neither intended nor suitable for use as heat-exchangers to be arranged behind the combustion chamber of heating boilers, have been taught, for example, by DE-A-925 721 and DE-A-3 014 506. The heat-exchangers according thereto are not of the type intended for arrangement behind the combustion chamber because the combustion chamber as such is contained therein and because the heating gases do not flow therethrough in the axial direction but rather in a spiral way. The same applies to a heat-exchanger of the type as described by EP-A-0 123 995. Reference is made to the verified state of art as evinced through the following literature references: U.S. Pat. No. 2 085 256; DE-A-95873; DE-A-288 039; DE-A-101 612 and DE-A-1 753 242. Although spirally coiled heat-exchangers of this type are advantageous as regards flow pattern, compact design and heat exchange, it has been found, quite amazingly, that such heat-exchangers do not seem to have introduced themselves as heat-exchangers integrated into the heating boiler casing behind the combustion chamber. Presumably, this is because it is extremely difficult, on the one hand, to close the narrow sides of the resultant channels of spiral configuration for the fluids participating in the heat exchange and, on the other hand, to spirally coil the participating sheet metals while maintaining the required distance from one another, i.e. without deformation.
Suggestions to achieve this are conveyed by a heating boiler according to DE-A-1 753 242 which, however, has also proved to be impracticable, or by a system according to the aforementioned DE-PS 925 721 which, however, is not suitable to be used as a heat-exchanger for arrangement behind the combustion chamber of a heating boiler because no open in-flow of the heating gases nor a straightforward flow thereof in the axial direction is permitted. Moreover, in this type of heat-exchanger exposed sheet metal edges arise on the in-flow side which would be subject to a high thermal strain. In addition, further spacers must be provided between the channels which, apparently, were unavoidable to enable a structure of this type to be spirally coiled. In addition, the bent edges directed towards the coil axis and predetermining the full width of the individual channels, during spiral coiling, form undulatory warpings because they face inwardly with the full width thereof so that welding difficulties are inevitably involved. Accordingly, the applicability of such spirally coiled heat-exchangers for arrangement behind the combustion chamber of heating boilers, due to the required and largely mechanical series production, stands and falls with an easy-to-manufacture design.